UCSB ECE 594 - Notes5 (8 pages)

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Notes5

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Pages:
8
School:
University of California, Santa Barbara
Course:
Ece 594 - High Speed Mixed Signal & Communications IC design

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Notes 5 ECE594I Fall 2009 E R Brown Free Space Power Coupling for Two Special Cases Radar and Radiometry Friis Transmission Formulation Marconi was the pioneer for a new generation of electrical engineers working in the area of wireless One of the truly brilliant amongst these was Friis working at Bell Laboratories in the 1920s and 30s Among other things Friis was the first to take advantage of the inherent nature of antennas as passive reciprocal components and treat the free space propagation between a transmit antenna and receive antenna as a two port link This was done first and foremost for the wireless communications link which we review here first to set the stage for the following RF and THz sensor i e radar and radiometer link formulation The first step in Friis formulation is the concept of an effective aperture Aeff for the receiving antenna Prec Aeff S inc r r p 1 where Prec is the power available to the antenna for delivery to a load S inc r r is the average Poynting vector for incoming radiation along the direction r r in the spherical coordinates centered at the receiving antenna and p is the polarization coupling efficiency Note that this expression applies only when S inc r r is aligned with the direction of the beam pattern maximum When there is misalignment another factor is required which is the just the receive beam pattern Prec Aeff Fr r r S inc r r p 2 Next we suppose that this received Poynting vector is generated by a second transmitting antenna We can relate the received power to the properties of the transmitting antenna by S inc r r S t r t t Prad Dt Ft t t P G F r in t t 2 t t r 2 4 r 4 r 93 3 Notes 5 ECE594I Fall 2009 E R Brown where the subscript t is for transmitting Prad is the total radiated power Pin is the power used to drive the transmitting antenna in the matched case equal to Prad t and t are the spherical angles in the spherical coordinate system centered at the transmitting antenna r is the power transmission function



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